Cemented paste backfill (CPB) consists of a mixture of fine particles, mainly consisting of tailings and cement dispersed in water. Therefore, it is necessary to introduce an intensive shearing force into the paste during mixing in order to maintain an equilibrium between agglomeration and dispersion. It is influential for the macroscopical fluidity and rheological properties when changes occur in the microstructure of CPB under shear. However, the research on how mixing affects the properties of CPB is still in its infancy. This paper puts an insight into the relation between the mixing intensity and the rheological behavior of the CPB. It can be demonstrated that two threshold mixing intensities exist in this process. After passing the first or lower threshold, the rheological parameters (yield stress and viscosity) of the paste decrease. After passing the second threshold, a continued increase is observed. The changes in rheological properties are connected with physical and chemical changes in the microstructure of the CPB. The results are discussed in light of the three concepts “structural breakdown”, “thixotropic breakdown”, and “thixotropic behavior” of rheological properties of CPB.

Since filling slurry is a cement-based material, viscosity-enhancing admixture exerts a significant effect on its rheological performance and mechanical properties. Viscosity-enhancing admixture can improve pipeline transportation performance and reduce pipeline wear during the filling process of a kilometer-deep mine by changing the plastic viscosity and yield stress of high-concentration filling slurries. In order to reveal the influence mechanism of viscosity-enhancing admixture on rheological performance in slurry, the influence of viscosity-enhancing admixture on the rheological performance of slurry is explored by adjusting viscosity-enhancing admixture dosage and conducting bleeding test, liquidity test, and rheological performance test. The extended DLVO theory is employed to analyze the mechanism of HPMC on the stability of filling slurry. The results show that compared with ordinary slurry, after adding HPMC and XG, the particles of filling slurry are prone to link to form a mesh structure. Besides, the increasing frictional force between particles results in a significant decrease in the bleeding rate and liquidity of the slurry. Such an effect becomes more obvious with the increase of viscosity-enhancing admixture dosage. Meanwhile, the overall effect of HPMC molecules is better than that of XG molecules since HPMC can reduce inter-particle repulsion and facilitate particle aggregation. The optimal dosage is about 0.1%, at which time the yield stress of the filling slurry increases from 89.236 to 160.06 Pa, the plastic viscosity increases from 0.296 to 1.063 Pa·s, and the compressive strength increases from 2.58 to 3.59 MPa in 28 days. The study reveals the influence of viscosity-enhancing admixture on the rheological performance of filling slurry and its evolution characteristics, which provides theoretical support for the development of filling resistance and wear reduction technology.

In China, cemented paste backfill (CPB) is a common treatment method after the exploitation of basic energy. The homogeneity of slurry influences the performance of CPB. However, the online monitoring and characterization of homogeneity lack relevant technologies and unified standards. This article discusses an online image analysis technique applied to the online monitoring of cemented paste backfill mixing, which is based on the evolution of the texture of images taken at the surface of the mixing bed. First, the grayscale distribution of the image obtained by the high-speed camera in the CPB preparation process was analyzed by Matlab and its variance (s²) was solved, and the texture features of the image were analyzed by the variance of grayscale distribution. Then, a homogeneity discriminant model ($c_{st}$) was established. The results show that the variance value of the grayscale distribution of the slurry image increases rapidly at first, then gradually decreases, and becomes stable in the final stage since it turns a constant value. When the s² value tends to be stable, the slurry gradually reaches homogenization, and the discriminant coefficient of paste homogenization based on the homogenization discriminant model reaches 0.05. The homogenization prediction of CPB proves to be consistent with the backfill performance comparison results. The evolution of the texture allows obtaining important information on the evolution of different formulations during mixing, which can be used for intelligent monitoring of CPB preparation process.